Process for cleaning petroleum refining equipment



Oct. 26, 1943.

w. B. KILLOUGH PROCESS FOR CLEANING PETROLEUM REFINING EQUIPMENT FiledFeb. 12, 1941 L Mug? w mm 6. 'INVENTOR.

BY fl If W ATTORNEY Patented Oct. 26, 1943 PROCESS FOR OFFICE REFININGEQUIPMENT Walton B. Killough, Baytown, Tex., assignor to Standard OilDevelopment Company, a corporation of Delaware Application February 12,1941, Serial Nb. 378,608

1 Claim. (01. 196-69) The present invention relates to improvements inthe art of treating hydrocarbons, and more particularly it relates toimprovements in the art of removing coke and coke-like materials fromrefinery equipment such as fractionating columns and the like.

Extended heat treatment of petroleum oils in refining operations resultsin decomposition of the hydrocarbons with the formation of polymerizedproducts of high molecular weight. These polymerized high-molecularweight hydrocarbon compounds and salts naturally occurring in the oil orresulting from the reaction of acidic water with ammonia or other vaporsthat may be injected in the oil stream to prevent corrosion of metallicsurfaces, usually deposit in conduits, on trays or on the walls of thechambers in which the heat treatment is taking place. It is thereforenecessary in conventional practice when a particular unit such as adistillation tower becomes fouled with the abovementioned deposits, toremove the tower from the production phase, steam the same and allow itto cool for safe entrance of workmen to remove the coke and polymerizedhydrocarbons. In vessels, such as fractionation towers having trays andbubble cap plates or other equipment which efiects an eflicient orintimate gas or liquid contact, the cleaning of the same is a tedious,timeconsuming, expensive operation which must be performed by hand.

The main object of my invention is to provide means for efficientlyremoving the coke-like polymerized hydrocarbons from a particular vesselsuch as a fractionating column in an improved manner, by the washingaction of a, hydrocarbon oil which is employed after the unit has beentakenofi the onstream operation.

It is my belief that during the refining of oils .in a particularvessel, such as a fractionating tower, heavy polymers accumulate on theplates around the bell caps. These heavy hydrocarbons are subjected toheat treatment, since it is believed that the velocity of the ascendingvapors is such that these polymerized hydrocarbons are carried up thetower by entraimnent and eventually are held between two or more plates.As time goes on, these compounds become heavier and heavier, that is tosay, they increase in molecular weight, but ordinarily remain fluid orin a suspended state until the temperature of the tower is reduced whenit is removed from the onstream operation. As the temperature of thetower is reduced and the normally fluid contents are removed, the heavypolymerized hydrocarbon or carbonaceous compounds precipitate and cementin a solid mass eifectively clogging the unit. This caked mass isextremely difficult to remove from a fractionation tower, particularlysince the construction of the tower is such that entry by workmentherein is difiicultand the restrict ed area frequentlyhinders use ofordinary cleaning procedures. It is therefore necessary for the workmento enter the tower after it has been steamed and cooled, to remove thecoke-like products by chipping and scraping. This method of removing thecaked mass is highly unsatisfactory from an economic standpoint, sincevaluable operating time is lost and the work constitutes a life hazard.i

As previously indicated, I have devised a process for cleaning petroleumrefining equipment of coke-like material and other deposits, and myinvention will be best understood by reference to the accompanyingdrawing which shows diagrammatically apparatus which I have selected toillustrate my invention.

The drawing shows a combination of a pipe still and a fractionatingcolumn, together with other accessory equipment, and I will now describemy process as used in cleaning the fractionating tower, with theunderstanding that the application of the process to this particulartype of equipment is purely illustrative and does not impose alimitation on my invention since heat exchangers and the like may alsobe cleaned by my cleaning process.

Referring in detail to the drawing, I represents a charging line throughwhich a hydrocarbon oil such as a crude petroleum is introduced into thesystem The charge oil is forced into coil 2 located in furnace 3, and inthe furnace it is heated to distillation temperature, say a temperatureof from about 525 F. to 685 F. The heated oil is withdrawn from coil 2in furnace 3 through line 4 and, by means of pump 5 and line 6, isintroduced into, fractionating tower 1. Light products are removedoverhead from fractionating tower 1 in line 8 and then discharged intocondenser 9 where condensable hydrocarbons are liquefied andsubsequently recovered by means of line H] connecting with receivingdrum ll. Liquefied hydrocarbons are recovered through line l2 whilenon-condensable hydrocarbons are recovered through line l3. A sidestreamfraction consisting of gas oil is removed from fractionating tower 1through line H may be cooled in cooler 28 and is collected in storagetank I5. Other side-stream fractions may be taken off from the tower, ifdesired,

guished in furnace 3 and the oil stream has been.

discontinued in line I, the oil remaining in tower l is pumped outthrough line 16 and a gas oil of 25 to 40 A. P. I. gravity isimmediately charged into the top of the said tower through" line I! andpump l8 which is in communication with gas oil storage drum E5. The oilin line ll't y is ordinarily provided at an initial temperature of about100 to 150 F. as'itenters the tower. Although the oil may be heated tohigher temperatures it is preferable to introduce the oil at therelatively low temperatures specified above. While the flushing oil isbeing introduced in the top of the tower, a sufficient amount of steamis injected into the bottom of tower I. through: line I9 to maintain thetemperature. of the flush ing oil at substantially the temperature atwhich it isintroduced. The flushing. oil, 1.. e., the gas oil, may beintroduced. into the. bottom. of the; tower as in the conventional flowof the crude oil during the refining operation, but it is. preferredtointroduce it into the top of'the tower. above the top plate and.permit. it. to circulate. downward. The gas oil. is circulated throughthe tower at a rate of about 100 t0.2l),000- gallons an hour dependingon the size of. the unit1be-- ing cleaned. While it is'preferred, forconvenience, to employ a gas oil obtained: duringz'the: onstreamoperation, I may use gas oilfrom. any source as the flushing oil.Circulationof theoil is maintained for 1 to 24 hours to obtairreffective cleaning. The oil .discharging from; the: tower through lineL6 isvisually examined; periodically to determine whetherv or not it;(IODIL tainssuspended bodies and; vwhenthe .oil. no long-- er containsthese suspendedbodies. the operat knows that substantially all of thecoke-like material has-been removed fromthe-tower; The oil leaving thetower through line It: may b.e.-dfi:-- verted by means of line to a-tankor sump: 2:!1 equipped with suitable baffles tolallow. settling ofsuspended materials flushed from the tower. After the suspendedmateriallhas settled, theoi'l may be recirculated by meansof lines221tar1da 23 through the furnace 3-heated; ifi' necessary; and pumpedagain to tower Tthroughlinesu'; pump- 5; and'lines 24- and H. Iheprecipitatedapolymerized matter orsalts are removed. from; the: tank orsump by anysuitable means asdredging, and this materialmay be mixed;material obtained through line it during".v the operating cycle tomanufacture a low grade fuel. such as bunker C fuel; On completion ofthe washing cycle as indicated by visual inspectionofthe washing oil,circulation of the n flushing medium through tower his then.discontinued; and the tower is-pumped free of 'gas 'oi l; Steam is againinjected-into the tower throughzlinei to remove waxy or otherhydrocarbons remaining on or wetting the sides of the tower l or thebubble caps and trays therein. After a final wash with water which isintroduced through line 25, the tower may be opened for inspection ifsuch is deemed necessary.

It is important that the sequence of steps and the several operationsdescribed be employed since, if the oil-washing operation is notfollowed by steaming and water washing, it has been found that thecleaning of the tower is not as effective as when all the stepsdescribed herein are employed.

In order to further illustrate my invention,

and particularly to disclose the nature of the flushing oil, thefollowing specific example is set forth fully describing gas oils whichI have found to be satisfactory in my process. It is understood, ofcourse, that the details enumerated in the following example are purelyillustrative, and other oils may be: used in place of those disclosed:

Erample A virgin gas'oil' of the following characteristics was used. inthe cleaning of a fractionating tower:

Gravity; a A. P. I. 38.2 Initial boiling point F 400* Final boilingpoint l=.' 620 Flash F 184- The-fractionating tower was removed fromser-' vice and, before the unit was allowed tocool, it'was' washed withvirgin gas oil' at a tempe'ra ture-of about F. for ten hours.The'washin'g was accomplished by pumping the gas oil at a rate of" 250barrels per hour to the top of the tower and allowing-it to flowdownward over the trays. The oil leaving the tower was not re circulatedbut was drawn' off and employed in another process; The tower was thensteamed for safety and opened for inspection; It was found to be"substantially free of coke like' de posits. The small amount, ofmaterial remain- 5 ingon" theplat'eswa's readily-removed without theusual scraping and chipping:

Many variations of my invention may be made by those familiarwit'h thisparticular art with out departing from the spirit of the said inven'-'tion.

.What Iclaimis:

A method for cleanings: fr'actionating column which comprises"introducing into" the column immediately after it has been removed fromonstream operation andiwhilef it is still hot, a gasoil' having agravity inith'e'. range from'about' 25 A. Pl I. to'aboutAO" A. P; I.,c'au'sin glsaidigafl oil to flow downwardlyithrough said'columnremoving. it from theb'ott'om thereofand introducing steam into thebottom of said column? during the downward flow or gas-oil? there"-through. 1

WALTON B. KIEIJOUGHi

